The heart is, in essence, a pump that is responsible for circulating blood throughout the body. In a normally functioning heart, such circulation is caused by the generation of electrical impulses that, for example, increase or decrease the heart rate and/or the force of contraction in response to the demands of the circulatory system. If the electrical signal becomes disturbed in some way, the efficient pumping action of the heart may deteriorate, or even stop altogether.
Disturbance in the regular rhythmic beating of the heart is a common disorder seen in heart disease. Irregular rhythms (arrhythmia) can be a minor annoyance, or may indicate a serious problem. For example, arrhythmias may indicate an underlying abnormality of the heart muscle, valves or arteries, and includes the situation where the heart is beating too slowly (bradycardia) and also where the heart is beating too rapidly (tachycardia).
One particular type of cardiac arrhythmia, known as atrial fibrillation (AF), is a common cardiac rhythm disorder which can affect the quality of a patient's life and may be associated with significant morbidity. Atrial fibrillation is characterized by a rapid disorganized rhythm of the upper chambers of the heart (the atria). Instead of a single wavefront of electrical activation during regular rhythm, AF consists of multiple coexistent wavefronts with random re-entry. The condition may happen by itself (lone AF), may be related with hypertension, valvular disease, or may arise following cardiac surgery.
The etiology of AF is varied and has been hypothesized in some cases to have a genetic component. While medication is effective to control AF in some patients, other primary treatment modalities, such as endocardial ablation or surgical intervention, are often necessary for effective treatment. For example, endovascular approaches may be used to create lesions using an ablation catheter to block intra-atrial conduction. Such primary treatments are not always satisfactory, however, as arrhythmias often reoccur in patients (20-50%) and ablation procedures may sometimes result in unwanted sequelae, such as pulmonary vein stenosis or drug inefficiency or side effects from the complementary pharmacological treatment, and thus additional secondary treatments such as additional ablation procedures may be necessary.
Another cause of significant morbidity and mortality is pulmonary arterial hypertension (PAH). PAH is a disease defined by a progressive elevation of pulmonary artery pressure and pulmonary vascular resistance, leading to right ventricular failure and death. Current therapies for PAH typically involve PDE-5 inhibitors, prostacyclins, endothelin receptor antagonists, and other agents for treating PAH. Such therapies have several drawbacks, however, including drug resistance, non-specific delivery to the pulmonary vasculature, and undesirable side effects.